Method and arrangement in a telecommunication system

ABSTRACT

The present invention relates to a method in a cellular communication system, for avoiding errors in a HARQ process, wherein an NDI flag is used both for indicating either semi-persistent scheduling, SPS activation or SPS retransmissions, and also for indicating, by toggling of the flag, a new transmission in dynamic scheduling mode. The method comprises the steps of receiving, in a scheduling message, an indication that dynamically scheduled transmission will take place; if a semi persistent resource has occurred for the same HARQ process since a previously received indication for dynamically scheduled transmission, then considering the NDI flag to be toggled regardless of the value of the NDI flag. Thus, if the condition is fulfilled, a UE will always regard the NDI flag as indicating or requesting a new data transmission.

FIELD OF THE INVENTION

The present invention relates to HARQ processes used for bothsemi-persistent scheduling and dynamically scheduled transmissions.

BACKGROUND

In order to achieve efficient link utilization, modern radio interfaceprotocols support Hybrid Automatic Repeat request (HARQ). A HARQtransmission is characterized by transmitting a channel-encoded (e.g.,by using a Turbo Code) data unit to the receiver. The receiver replieswith a feedback signal that indicates either the successful reception(ACK) or the unsuccessful reception (NACK) In case of a received NACK,the data sender retransmits the same or another so-called redundancyversion of the same data unit. The HARQ receiver soft-combines allreceived redundancy versions for the particular data unit. For eachterminal there is one HARQ entity in the transmitting unit, e.g. a basestation such as an eNodeB and one HARQ entity in the receiving unit,e.g. a user equipment, UE. Each HARQ entity hosts of a number ofparallel HARQ processes.

The LTE radio access is intended to use scheduled transmission, i.e.,shared transmission resources can be assigned to users on a very shorttime scale. The scheduler deciding on the resource allocation for uplinktransmission is located in the base station. The main mode of operationfor the scheduler in LTE is assumed to be dynamic scheduling whereby thebase station transmits scheduling messages, i.e. uplink grants ordownlink assignments, to the UEs to indicate which physical resourcesthey have been allocated for uplink transmission and downlink reception.The base station also indicates how the data transmission shall be codedand modulated in both uplink and downlink. For downlink, where anasynchronous HARQ is assumed, information comprising HARQ process id andredundancy version is included on a control channel as part of thescheduling assignment. Since for the uplink a synchronous HARQ protocolis assumed, the employed HARQ process ID and the redundancy version arecoupled to the transmission timing. Thus this information is neithersent in the uplink grant nor in parallel to the uplink transmission onan uplink control channel. Instead, both sender and receiver can deriveprocess ID and redundancy version from the transmission status.

The LTE MAC specification supports two different scheduling modes.Dynamic scheduling is the mode in which each initial (new) transmissionof data is indicated via a control channel (PDCCH, Physical DownlinkControl Channel) Semi-persistent scheduling (SPS) is the mode in whicheach initial (new) transmission is made on pre-assigned resources, i.e.the radio resources are known in the time and frequency domain.

The SPS technique thus makes assignments (downlink data transmission) orgrants (uplink data transmission) for the first transmission of datasuperfluous and thus saves control signaling resources.

The dynamic scheduling requires relatively much signaling overhead. Inorder to reduce this overhead, it has been decided in 3GPP to support socalled semi-persistent scheduling (SPS). In SPS the periodicity of ascheduling grant (uplink) or scheduling assignment (downlink) isconfigured via an RRC, Radio Resource Control, protocol. The SPS isstarted by transmitting a grant/assignment on the PDCCH.

In LTE the identification of UEs on the PDCCH is done by reusing theCRCr Cyclic Redundancy Check r bits. The UE identity (typically C-RNTI)is scrambled with the CRC such that when a message is transmitted onPDCCH only the UE that de-scrambles with the correct C-RNTI will have asuccessful CRC. Other UEs will scramble with a different C-RNTI andtheir CRC will not be successful. Thus they will discard the command onthe PDCCH. For SPS a separate C-RNTI is used, the SPS C-RNTI. Thus theUE can distinguish if a received assignment/grant on the PDCCH is adynamic grant/assignment or a semi persistent grant/assignment based onwhich C-RNTI is used. The base station is responsible for assigning thedifferent C-RNTIs uniquely to the UEs.

Semi-persistent scheduling operation thus has the followingcharacteristics:

-   -   Configuration of SPS is done via the RRC protocol r i.e′ r    -   the resources that might be used for new transmissions (opposed        to HARQ retransmissions) are configured.    -   If SPS is configured r the actual activation is done with a        PDCCH message. Thus r a PDCCH signal is used to activate the SPS        resource usage with the RRC-configured parameters.    -   New HARQ transmissions are transmitted at the given SPS resource        allocations.    -   Required retransmissions are dynamically scheduled (but still        the HARQ process is a semi-persistent process. This should not        be confused with a dynamic HARQ transmission where the first        transmission is dynamically scheduled) i.e., a PDCCH message is        used to indicate the retransmission.

A HARQ process used for semi-persistent scheduling can still be used fordynamically scheduled transmission, i.e., a certain HARQ process is nottied to either SPS or dynamic scheduling. For example, if a dynamic HARQprocess is still on-going and a PDCCH SPS activation is received(indicated by the SPS C-RNTI), the dynamic process is terminated and theSPS HARQ process overrides existing data, and since the transmission ismade on pre-assigned resources, no PDCCH message is sent for thesubsequent SPS transmission that follows the SPS activation. On theother hand, if an SPS process is in use and a dynamic HARQ transmissionis scheduled (indicated by the C-RNTI), a PDCCH message must be sent.The PDCCH message, comprising a scheduling message, i.e. an uplink Grantor a downlink Assignment, includes a field denoted as NDI (New DataIndicator). The field size is currently 1 bit. The NDI bit is animportant indicator to resolve HARQ error cases and has been originallyintroduced for the dynamic scheduling mode. For dynamic scheduling, i.e.where the first transmission is dynamically scheduled, the NDI bit istoggled with each new transmission. Thus the value can be either 0 or 1for a new transmission and it will remain the same value forcorresponding HARQ retransmissions for a specific MAC Protocol DataUnit, PDU. For downlink transmission this allows the UE to detectwhether a new HARQ transmission starts or whether a retransmission is tobe expected.

Consequently, it either flushes the HARQ buffer (in case of a newtransmission) or it attempts to soft-combine the retransmission with theexisting content in the soft-buffer.

For uplink transmission the NDI indicates if the UE is expected toperform a retransmission of the previously transmitted data or if itshall flush the process and obtain new data from higher layers fortransmission in the dynamically assigned resource. However, it has beendecided that SPS activation will use the value NDI=O and SPSretransmissions will use the value NDI=l in the corresponding PDCCHsignal. Thus, there exist two different interpretations of the NDI bitdepending on the RNTI value used for addressing a User Equipment, UE, onthe PDDCH. If the SPS C-RNTI is used, the NDI determines whether SPSwill be activated or whether a retransmission is sent.

For dynamically scheduled HARQ processes, the NDI has a differentmeaning as previously explained. The decision to use the NDI bit for SPSactivation and retransmission indication for SPS leads to problems,since a new interpretation is introduced.

When a HARQ process associated with SPS resources should be temporarilyused by a dynamically scheduled HARQ transmission, the NDI value can notbe applied as in the case where the HARQ process is exclusivelyscheduled dynamically.

Since the NDI bit is stored in relation to the HARQ process and the HARQprocess can be either an SPS process or a dynamically scheduled process,the current specification would lead to an erroneous behavior since theNDI relating to SPS would be interpreted in the context of the dynamicHARQ process, when the first dynamically scheduled HARQ transmissiontakes place in a process that has been used based on SPS resourcesbefore.

SUMMARY

It is the object of this invention to mitigate the above mentionedproblems.

One aspect of the invention relates to a method in a user equipment, UE,in connection with a base station in a cellular communication system,for avoiding errors in a HARQ process, wherein an NDI flag is used bothfor indicating either semi-persistent scheduling, SPS, activation or SPSretransmissions, and for indicating, by toggling of the flag, a newtransmission in dynamic scheduling mode. The method comprises the stepsof:

-   -   receiving, in a scheduling message, an indication that a        dynamically scheduled transmission will take place;    -   if a semi persistent resource has occurred for the same HARQ        process since a previously received indication for dynamically        scheduled transmission, then considering the NDI flag to be        toggled regardless of the value of the NDI flag.

Thus, according to an embodiment of the invention, a previousdynamically scheduled NDI value, received before the HARQ process wasused for Semi Persistent Scheduling, SPS, is ignored by the UE, wherebyany NDI value, received in a first indication for dynamic scheduling ofa transmission after the HARQ process has been used for SPS, is adopted,whereby the NDI flag is regarded as toggled.

Said scheduling message may comprise an uplink grant, by means of whichthe base station requests a new data transmission from the UE. The UEmay use one of the following as an indication that dynamically scheduledtransmission will take place: the scheduling message is addressed to theC-RNTI or to the Temporary C-RNTI, or was received in a Random Accessresponse.

Said scheduling message may alternatively comprise a downlinkassignment, by means of which the base station indicates a new datatransmission to the UE. The UE may use one of the following as anindication that dynamically scheduled transmission will take place: thescheduling message is addressed to the C-RNTI or to the TemporaryC-RNTI, or to the RA-RNTI, i.e. the Random Access RNTI.

The UE may receive the scheduling message on a Physical Downlink ControlChannel, PDCCH.

A second aspect of the invention relates to a User Equipment, UE,connectable to a base station in a cellular communication system, saidUE being configured to avoid errors in a HARQ process, in which an NDIflag is used both for indicating either semi-persistent scheduling, SPS,activation or SPS retransmissions, and for indicating, by toggling ofthe flag, a new transmission in dynamic scheduling mode. The UEcomprises

-   -   a transceiver unit configured to receive, in a scheduling        message, an indication that dynamically scheduled transmission        will take place    -   a processing unit configured to check if a semi persistent        resource has occurred for the same HARQ process since a        previously received indication for dynamically scheduled        transmission and to consider the NDI flag to be toggled        regardless of the value of the NDI flag if said condition is        fulfilled.

A third aspect of the invention relates to a method in a base station inconnection with a UE in a cellular communication system, for avoidingerrors in a HARQ process, wherein an NDI flag is used both forindicating semi-persistent scheduling, SPS, activation and SPSretransmissions and for indicating, by toggling of the flag, a newtransmission in dynamic scheduling mode. The method comprises the stepsof

-   -   indicating, in a scheduling message to the UE that dynamically        scheduled transmission will take place;    -   if a semi persistent resource has occurred for the same HARQ        process since a previous indication to the UE for dynamically        scheduled transmission, then setting the NDI flag to any value        and considering the NDI flag to be toggled regardless of the        value of the NDI flag.

Thus, according to this embodiment, the method performed by the basestation comprises the step of setting the NDI flag to 0 or 1 or anarbitrary value, whereby the UE will regard the NDI value as toggled,independent of the value of the flag.

A fourth aspect of the invention relates to a base station connectablewith a UE in a cellular communication system, configured to avoid errorsin a HARQ process, the base station being configured to use, in a HARQprocess in communication with a UE, an NDI flag both for indicatingeither semi-persistent scheduling, SPS, activation or SPSretransmissions, and for indicating, by toggling of the flag, a newtransmission in dynamic scheduling mode. The base station comprises ascheduling unit configured to schedule a dynamic transmission;

-   -   a transceiver unit configured to transmit in a scheduling        message to said UE, an indication that dynamically scheduled        transmission will take place;    -   a processing unit configured to check if a semi persistent        resource has occurred for the same HARQ process since a previous        indication to the UE for dynamically scheduled transmission and        to set the NDI flag to any value and consider the NDI flag to be        toggled regardless of the value of the NDI flag if said        condition is fulfilled.

The base station may for example be an eNodeB. Thus, said base stationcomprises in this embodiment means for setting a value of the flag (NDI)in a first decision for dynamic scheduling after the HARQ process hasbeen used for SPS to 0 or 1 or an arbitrary value.

According to embodiments of the invention applied in downlink, a UserEquipment (UE) performs the check for the previous usage of the HARQprocess, whereby the risk that the HARQ receiver might interpret a newtransmission as a retransmission, which could lead to errors, isavoided. Other objects, advantages and novel features of the inventionwill become apparent from the following detailed description of theinvention when considered in conjunction with the accompanying drawingsand claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features and advantages of theinvention will be apparent from the following detailed description ofpreferred embodiments as illustrated in the drawings.

FIG. 1 shows a flowchart for downlink according to an embodimentperformed by a UE;

FIG. 2 shows a flowchart for uplink according to an embodiment performedby a UE;

FIG. 3 shows a flowchart for downlink according to an embodimentperformed by a base station;

FIG. 4 shows a flowchart for uplink according to an embodiment performedby a base station;

FIG. 5 shows a schematic illustration of a User Equipment according toan embodiment of the invention.

FIG. 6 shows a schematic illustration of a base station according to anembodiment of the invention.

FIG. 7 shows a flowchart for downlink according to an alternativeembodiment performed by a UE;

FIG. 8 shows a flowchart for downlink according to an alternativeembodiment performed by a base station;

FIG. 9 shows a flowchart for uplink according to an alternativeembodiment performed by a base station;

FIG. 10 shows a flowchart for uplink according to an alternativeembodiment performed by a UE.

DETAILED DESCRIPTION

The present invention can be exemplified in the following non-limitingdescription of embodiments of the invention.

A solution to the problem of having two different interpretations of theNDI bit depending on the C-RNTI value used for addressing a UserEquipment, UE, is to ignore the previous dynamically scheduled NDIvalue, to adopt any NDI received in a first PDCCH message for dynamicscheduling after the HARQ process has been used for SPS and to interpretit as new transmission attempt rather than a retransmission.

An additional condition that is required to avoid HARQ errors is thatthe PDCCH message is the first PDCCH message for dynamic schedulingafter SPS deactivation.

It is possible to start either with a specific NDI value/e.g. always 1or always 0/or an arbitrary value of 0 and 1.

It is foreseen that the DE checks whether the NDI value in the receivedPDCCH downlink assignment or uplink grant was incremented (assuming amodulo 2 operation) or, equivalently, toggled compared to the previousvalue. That is, the received NDI value has been toggled when the NDIvalue is 1 or 0 compared to a previous value of 0 or 1, respectively.

According to the embodiment of the invention described above, this checkis only performed when the HARQ process was occupied in the previoustransmission by a dynamically scheduled transmission. If, on the otherhand, the resources have been previously used for a semi-persistenttransmission and now it is detected that a dynamic transmission shall beperformed, then the UE should, according to this embodiment of theinvention, consider the NDI value as toggled (regardless of the NDIvalue in the received PDCCH assignment or grant) and for the uplink caseperform a new transmission, and for the downlink case, treat thereceived transmission as a new transmission.

This embodiment could be implemented according to the following:

For Downlink:

DL Assignment Reception

Downlink assignments transmitted on the PDCCH indicate if there is atransmission on the DL-SCH for a particular UE and provide the relevantHARQ information.

When the UE has a C-RNTl, Semi-Persistent Scheduling CRNTl, or TemporaryC-RNTl, the UE shall for each TTl during Active Time, for each TTl whena Random Access Response or contention Resolution is expected and foreach TTl for which a DL assignment has been configured:

-   -   if a downlink assignment for this TTl has been received on the        PDCCH for the UE's C-RNTl, or Temporary C-RNTl:    -   if a Semi Persistent resource has occurred for the same HARQ        process since the previous received downlink assignment for the        UEs C-RNTl:    -   consider the NDl to be toggled regardless of the value of the        NDl;    -   indicate the presence of a downlink assignment and deliver the        associated HARQ information to the HARQ entity for this TTl.

For downlink there are in principle three ways an SPS resource canoccur, namely

-   -   a DL assignment for a UE's Semi Persistent Scheduling RNTl        indicating a new SPS transmission, has been received, thus a        Semi Persistent Scheduling resource is (re-)        configured/activated;    -   a DL assignment for a UE's Semi Persistent Scheduling C-RNTl        indicating a Semi Persistent Scheduling HARQ retransmission;    -   the recurrence of a configured SPS downlink assignment and the        associated SPS resource occurring according to the periodicity        of a scheduling downlink assignment after the (re-)        configuration/activation.        For Uplink:        UL Grant Reception

In order to transmit on the UL-SCH the UE must have a valid uplink grant(except for non-adaptive HARQ retransmissions) which it may receivedynamically on the PDCCH or in a Random Access Response or which may beconfigured semi-persistently. To perform requested transmissions, theMAC layer receives HARQ information from lower layers. When the UE has aC-RNTI, Semi-Persistent Scheduling C-RNTI, or Temporary C-RNTI, the UEshall for each TTl:

-   -   if an uplink grant for this TTl has been received on the PDCCH        for the UE's C-RNTI, Semi-Persistent Scheduling C-RNTI or        Temporary C-RNTI; or    -   if an uplink grant for this TTl has been received in a Random        Access Response:        -   if a Semi Persistent resource has occurred for the same HARQ            process since the previous received uplink grant for the UEs            C-RNTI:            -   consider the NDI to be toggled regardless of the value                of the NDI;            -   deliver the uplink grant and the associated HARQ                information to the HARQ entity for this TTl.

Also for uplink there are in principle three ways an SPS resource canoccur, namely

-   -   an UL grant for a UE's Semi Persistent Scheduling CRNTI        indicating a new SPS transmission, has been received, thus a        Semi Persistent Scheduling resource is (re-)        configured/activated;    -   an UL grant for a UE's Semi Persistent Scheduling CRNTI        indicating a Semi Persistent Scheduling HARQ retransmission;    -   the recurrence of a configured SPS uplink grant and the        associated SPS resource occurring according to the periodicity        of a scheduling uplink grant after the (re)        configuration/activation.

According to the current E-UTRA standard specification for the MACprotocol, TS 36.321 v8.2.0, the identifier that a dynamic transmissionshall be performed is the C-RNTI (Cell Radio Network TemporaryIdentity), Temporary C-RNTI or RARNTI value.

If, on the other hand, the SPS C-RNTI is received, a retransmission forthe semi-persistent process shall be performed. HARQ is asynchronous indownlink, meaning that the scheduler is free to schedule any HARQprocess at any given point in time. Therefore it has to signal the HARQprocess ID.

In uplink the HARQ is synchronous, meaning that the HARQ process has atiming pattern. Thus the HARQ process ID is known without PDCCHsignaling.

FIG. 1 shows an embodiment of the invention for downlink performed by aUE. In a first step, the UE receives a DL assignment on PDCCH. The RNTIthat is used for this assignment indicates a dynamically scheduledtransmission. The HARQ process ID is included in the PDCCH assignmentand the UE retrieves it from there and selects the correct process. Ifthe previous reception, HARQ process was on an SPS resource, RX, for theparticular then the UE regards the NDI flag as toggled, meaning that thereceived transmission is treated as a new transmission.

FIG. 2 shows an embodiment of the invention for uplink performed by aUE. In a first step, an UL grant is received on the PDCCH. The RNTI thatis used for this grant indicates a dynamically scheduled transmission.The HARQ process ID is coupled to the timing of the grant and the UEknows which process it should use at a given TTl, Transmission TimeInterval. If the previous transmission, TX, for the particular HARQprocess was on an SPS resource, then the UE regards the NDI flag astoggled and in the next step indicates uplink grant and HARQ informationto the HARQ entity for the TTl in question.

FIG. 3 shows an embodiment of the invention for downlink performed by abase station. In a first step, a dynamic downlink transmission isscheduled. The RNTI that is used for the downlink assignment to the UEindicates a dynamically scheduled transmission. If the previoustransmission, TX, for the particular HARQ process was on an SPSresource, then the NDI value is set to either 1 or 0, or an arbitraryvalue of 0 and 1. Thereafter the base station proceeds with thetransmission of downlink assignment and HARQ transmission.

FIG. 4 shows an embodiment of the invention for uplink performed by abase station. In a first step, a dynamic uplink transmission isscheduled. The RNTI that is used for the uplink grant indicates adynamically scheduled transmission. If the previous reception, RX, forthe particular HARQ process was on an SPS resource, then the NDI valueis set to either 1 or 0, or an arbitrary value of 0 and 1. Thereafterthe base station proceeds with uplink grant transmission. In theembodiments shown in FIGS. 3 and 4, the base station thus adopts the setNDI value as status for the respective HARQ process such that it is ableto send the same value again if a retransmission is requested. For thatpurpose the base station stores the NDI value as part of the HARQ statusinformation.

FIG. 5 illustrates schematically a user equipment 500 according to anembodiment of the invention, comprising a transceiver 510, via which theUE receives a downlink assignment or an uplink grant from the basestation that the UE is connected to. The UE can for example receive suchmessages on a Physical Downlink Control Channel, PDCCH. A processingunit 520 is configured to check if a semi persistent resource hasoccurred for the particular HARQ process since a previously receiveddownlink assignment or uplink grant. The processing unit is furthermoreconfigured to consider the NDI flag that is included in the downlinkassignment or uplink grant to be toggled regardless of the value of theNDI flag if said condition is fulfilled. Thus, by considering the NDIflag as toggled, the UE will for the downlink case treat a received HARQtransmission as a new transmission. For the uplink case, the UE willindicate uplink grant and deliver the associated HARQ information to theHARQ entity for this TTl. Thus, the UE comprises in this embodimentmeans for adopting a value of the flag (NDI) received in a firstindication for dynamic scheduling after the HARQ process has been usedfor SPS, and means for regarding said NDI flag as toggled.

FIG. 6 illustrates schematically a base station 600 according to anembodiment of the invention, adapted to communicate with one or moreuser equipments, UEs. The base station comprises a scheduling unit 601configured to schedule a dynamic uplink or downlink transmission from orto a UE connected to said base station. The base station furthermorecomprises a transceiver unit 610 configured to transmit in a downlinkassignment or an uplink grant to said UE, an indication that adynamically scheduled transmission will take place. A processing unit620 is configured to check if a semi persistent resource has occurredfor the particular HARQ process since a previously received downlinkassignment or uplink grant and to set an NDI value that the UE (500)will regard as toggled regardless of the value of the NDI flag if saidcondition is fulfilled.

An alternative solution to the problem of having two differentinterpretations of the NDI bit depending on the RNTI value used foraddressing a User Equipment, UE, could be to store the last NDI value ofthe last dynamically scheduled transmission attempt at the receiver andthe sender side for as long as the process is associated with asemi-persistent resource allocation. After using the HARQ process forsemi-persistent scheduling, the stored NDI value needs to be retrievedwhen the SPS usage is revoked and dynamic scheduling is applied, suchthat a dynamically scheduled HARQ transmission should take place. Thus,according to this embodiment, the dynamic NDI value needs to be storedat both the sender and receiver, and retrieved when the HARQ process isfor the first time used as dynamic process after it has been used by SPSbefore. FIG. 7 shows this alternative embodiment of the invention fordownlink performed by a UE. The UE receives a DL assignment on PDCCH ina first step. The HARQ process ID is included in the PDCCH assignmentand the DE retrieves it from there and selects the correct process.

If the previous reception, RX, for the particular HARQ process was on anSPS resource, then the UE retrieves the stored dynamic NDI value from amemory before the last step where it indicates downlink assignment andHARQ information to the HARQ process for the TTl in question.

FIG. 8 shows this alternative embodiment of the invention for downlinkperformed by a base station such as an eNodeB. In a first step, adynamic downlink transmission is scheduled. If the previoustransmission, TX, for the particular HARQ process was on an SPSresource, then the base station retrieve a stored dynamic NDI value froma memory and thereafter proceeds with downlink assignment and HARQtransmission.

FIG. 9 shows this alternative embodiment of the invention for uplinkperformed by a base station. In a first step, a dynamic uplinktransmission is scheduled. If the previous reception, RX, for theparticular HARQ process was on an SPS resource, then the base stationretrieves a stored dynamic NDI value from a memory and thereafterproceeds with uplink grant transmission.

Thus, the method performed by the base station according to thisalternative embodiment comprises the step of storing the last NDI valuethat is used for dynamic scheduling for as long as the process isassociated with a semi-persistent resource allocation. The stored NDIvalue is retrieved when the SPS usage is revoked and dynamic schedulingis applied.

FIG. 10 shows this alternative embodiment of the invention for uplinkperformed by a UE. The UE receives an UL grant on PDCCH in a first step.The HARQ process ID is included in the PDCCH grant and the UE retrievesit from there and selects the correct process. If the previoustransmission, TX, for the particular HARQ process was on an SPSresource, then the UE retrieves the stored dynamic NDI value from amemory before the last step where it indicates uplink grant and HARQinformation to the HARQ process for the TTl in question. A UE may insaid alternative embodiment comprise means such as a memory for storingthe value of the flag (NDI) for as long as the HARQ process isassociated with a semi-persistent resource allocation and means such asa processing unit for retrieving the stored NDI value when the SPS usageis revoked and dynamic scheduling is applied.

A base station according said alternative embodiment may comprise meansfor storing the value of the flag (NDI) for as long as the HARQ processis associated with a semi-persistent resource allocation and means forretrieving the stored NDI value when the SPS usage is revoked anddynamic scheduling is applied.

Yet another alternative solution to the problem would be to separate theHARQ processes for SPS and dynamic scheduling in a way that they stilluse the same HARQ process ID, but that the respective RNTls, i.e. theSPS C-RNTI or the C-RNTI, are used as additional pointers to therealization of the HARQ process, either for SPS or for dynamicscheduling. This includes that state variables belonging to each HARQprocess are treated independent of each other. In essence, the instancesof the two HARQ processes could be operated simultaneously andindependently of each other. For example, there would be both an SP-NDIvariable and a normal NDI variable for dynamic scheduling. Similarly,the soft buffer of both processes would be used independently.

The present invention may be carried out in other ways than thosespecifically set forth herein without departing from essentialcharacteristics of the invention. The present embodiments are to beconsidered in all respects as illustrative and not restrictive

Abbreviations

PDCCH—Physical Downlink Control Channel

HARQ—Hybrid ARQ

SPS C-RNTI—Semi-Persistent Scheduling Cell Radio Network TemporaryIdentifier

RA-RNTI—Random Access Identifier Radio Network Temporary

C-RNTI—Cell Radio Network Temporary Identifier

NDI—New Data Indicator

REFERENCES

-   E-UTRA MAC Specification 36.321 v8.2.0

What is claimed:
 1. A method for processing scheduling information at auser equipment (UE) in a cellular communication system, the methodcomprising: receiving a scheduling message indicating an allocation oftransmission resources for an uplink transmission associated with afirst Hybrid Automatic Repeat reQuest (HARQ) process; interpreting thescheduling message as scheduling a new data transmission based on atoggled new data indicator (NDI) flag in the scheduling message, if thescheduling message is addressed to an identifier that is associated withdynamic scheduling for the UE and a most recent previous transmissionfor the first HARQ process; storing the value of the NDI flag; andtransmitting the new transmission for the first HARQ process inaccordance with the scheduling message.
 2. The method of claim 1,wherein: receiving a scheduling message comprises receiving a downlinkassignment on a Physical Downlink Control Channel (PDCCH) indicating anallocation of transmission resources for a downlink transmission to theUE; and receiving a new data transmission comprises receiving a new datatransmission over a Physical Downlink Shared Channel (PDSCH) on downlinktransmission resources indicated by the downlink assignment.
 3. Themethod of claim 1, wherein: receiving a scheduling message comprisesreceiving an uplink grant on a Physical Downlink Control Channel (PDCCH)indicating an allocation of transmission resources for an uplinktransmission by the UE; and receiving a new data transmission comprisestransmitting a new data transmission over a Physical Uplink SharedChannel (PUSCH) on uplink transmission resources indicated by the uplinkgrant.
 4. The method of claim 1, further comprising, after receiving ortransmitting the new data transmission for the first HARQ process on thedynamically-scheduled resource, determining whether a second schedulingmessage received for the dynamically-scheduled transmission for thefirst HARQ process relates to a new transmission or a re-transmissionbased on whether a current value of the NDI flag received in the secondscheduling message is toggled.
 5. The method of claim 1, furthercomprises comparing the stored value of the NDI flag with the currentvalue of the NDI flag received in the second scheduling message for thedynamically-scheduled transmission to recognize if the NDI flag istoggled.
 6. A user equipment (UE) in a cellular communication system,the UE comprising: a receiver for receiving a scheduling messageindicating an allocation of transmission resources for an uplinktransmission associated with a first Hybrid Automatic Repeat reQuest(HARQ) process; a processor for interpreting the scheduling message asscheduling a new data transmission based on a toggled new data indicator(NDI) flag in the scheduling message, if the scheduling message isaddressed to an identifier that is associated with dynamic schedulingfor the UE and a most recent previous transmission for the first HARQprocess; a storage unit for storing the value of the NDI flag; and atransmitter for transmitting the new transmission for the first HARQprocess in accordance with the scheduling message.
 7. The UE of claim 6,wherein: the receiver further receives a downlink assignment on aPhysical Downlink Control Channel (PDCCH) indicating an allocation oftransmission resources for a downlink transmission to the UE, andreceives a new data transmission over a Physical Downlink Shared Channel(PDSCH) on downlink transmission resources indicated by the downlinkassignment.
 8. The UE of claim 6, wherein: the receiver receives anuplink grant on a Physical Downlink Control Channel (PDCCH) indicatingan allocation of transmission resources for an uplink transmission bythe UE, and receives a new data transmission comprises transmitting anew data transmission over a Physical Uplink Shared Channel (PUSCH) onuplink transmission resources indicated by the uplink grant.
 9. The UEof claim 6, wherein the processor determines whether a second schedulingmessage received for the dynamically-scheduled transmission for thefirst HARQ process relates to a new transmission or a re-transmissionbased on whether a current value of the NDI flag received in the secondscheduling message is toggled.
 10. The method of claim 6, furthercomprises comparing the stored value of the NDI flag with the currentvalue of the NDI flag received in the second scheduling message for thedynamically-scheduled transmission to recognize if the NDI flag istoggled.